Vehicle control system and vehicle control method

ABSTRACT

A vehicle control system and method is applied to a vehicle including: a continuously variable transmission for changing a speed ratio continuously that is disposed between an input shaft and an output shaft; a geared transmission that is disposed parallel to the continuously variable transmission, and that is adapted to establish a speed ratio that cannot be established by the continuously variable transmission; and a friction clutch that is brought into engagement to switch a torque transmission route from a route including the geared transmission to a route including the continuously variable transmission. The vehicle control system is configured to start a speed change operation of the continuously variable transmission before a commencement of clutch-to-clutch shifting between the friction clutches when switching the torque transmission route from the route including the geared transmission to the route including the continuously variable transmission.

TECHNICAL FIELD

The present invention relates to a control system and a control method for a vehicle in which a geared transmission adapted to establish fixed gear stages and a continuously variable transmission adapted to change a speed ratio continuously are arranged parallel to each other between an input shaft and an output shaft.

BACKGROUND ART

Vehicles in which a geared transmission and a continuously transmission are arranged parallel to each other between an input shaft to which a power of the prime mover is delivered and an output shaft are known in the conventional art. The geared transmission is adapted to select a fixed gear stage from a plurality of gear stages, and the continuously variable transmission is adapted to change a speed ratio continuously. In the vehicle of this kind, a clutch is arranged to switch a power transmission route between a route including the geared transmission and a route including the continuously variable transmission. It is also known in the art that the geared transmission is adapted to establish a fixed gear stage that cannot be established by the continuously variable transmission. Various kinds of control systems and methods for switching the power transmission route in this kind of vehicles have been proposed.

For example, Japanese Patent Laid-Open No. 03-061762 describes a control system and a control method for the vehicle in which the geared transmission and a continuously variable transmission are arranged parallel to each other between the input shaft and the output shaft. According to the teachings of Japanese Patent Laid-Open No. 03-061762, a speed change operation of the continuously variable transmission is inhibited until completion of a shifting of the power transmission route from the route including the geared transmission to the route including the continuously variable transmission, so as to maintain a speed ratio on the continuously variable transmission to a maximum ratio from a commencement to a completion of the speed change operation. For this reason, the vehicle is allowed to be propelled utilizing a decelerating effect of the maximum speed ratio when the power transmission route to the route including the continuously variable transmission.

However, according to the teachings of Japanese Patent Laid-Open No. 03-061762, the continuously variable transmission is allowed to change a speed ratio thereof from a point at which the power transmission route is switched. That is, the speed ratio may be changed stepwise before and after the switching operation of the power transmission route. For this reason, a speed change operation may not be performed smoothly. In addition, it may take time to achieve a target speed ratio calculated based on a vehicle speed.

DISCLOSURE OF THE INVENTION

The present invention has been conceived noting the foregoing technical problem, and it is therefore an object of the present invention is to provide a control system and a control method for vehicles configured to change a speed ratio efficiently when switching a power transmission route from a route including a geared transmission to a route including a continuously variable transmission.

According to one aspect of the present invention, there is provided a vehicle control system comprising: a continuously variable transmission for changing a speed ratio continuously that is disposed between an input shaft to which torque of a prime mover is applied and an output shaft; a geared transmission that is disposed parallel to the continuously variable transmission, and that is adapted to establish a speed ratio that cannot be established by the continuously variable transmission; a first friction clutch that is brought into engagement during propelling the vehicle by delivering torque through a route including the geared transmission and brought into disengagement during propelling the vehicle by delivering torque through a route including the continuously variable transmission; and a second friction clutch that is brought into engagement during propelling the vehicle by delivering torque through the route including the continuously variable transmission and brought into disengagement during propelling the vehicle by delivering torque through the route including the geared transmission. In order to achieve the above-explained objective, according to the present invention, the vehicle control system is configured to start a speed change operation of the continuously variable transmission before a commencement of clutch-to-clutch shifting between the friction clutches when switching the torque transmission route from the route including the geared transmission to the route including the continuously variable transmission.

The vehicle control system may start the speed change operation of the continuously variable transmission when switching the torque transmission route, before starting disengagement of the first friction clutch or before starting engagement of the second friction clutch.

The vehicle control system may execute the clutch-to-clutch shifting between the friction clutches while changing a speed ratio of the continuously variable transmission.

The vehicle control system may stop the speed change operation of the continuously variable transmission before a commencement of an inertia phase resulting from the clutch-to-clutch shifting between the friction clutches.

The vehicle control system may restart the speed change operation of the continuously variable transmission before completion of the clutch-to-clutch shifting between the friction clutches.

The vehicle control system may also restart the speed change operation of the continuously variable transmission if a torque transmitting capacity of the second friction clutch is greater than a predetermined value.

Optionally, a the continuously variable transmission may include a pair of pulleys, and the vehicle control system may restart the speed change operation of the continuously variable transmission when a difference between a rotational speed of the output shaft and a rotational speed of driven pulley of the continuously variable transmission is smaller than a predetermined value.

In addition, each of the first friction clutch and the second friction clutch individually may include a hydraulic actuator; and the vehicle control system may restart the speed change operation of the continuously variable transmission when a hydraulic pressure of the second friction clutch is higher than a predetermined level.

According to another aspect of the present invention, there is provided a control method for a vehicle comprising: a continuously variable transmission for changing a speed ratio continuously that is disposed between an input shaft to which torque of a prime mover is applied and an output shaft; a geared transmission that is disposed parallel to the continuously variable transmission, and that is adapted to establish a speed ratio that cannot be established by the continuously variable transmission; a first friction clutch that is brought into engagement during propelling the vehicle by delivering torque through a route including the geared transmission and brought into disengagement during propelling the vehicle by delivering torque through a route including the continuously variable transmission; and a second friction clutch that is brought into engagement during propelling the vehicle by delivering torque through the route including the continuously variable transmission and brought into disengagement during propelling the vehicle by delivering torque through the route including the geared transmission. In order to achieve the above-explained objective, according to the present invention, the vehicle control method is characterized by starting a speed change operation of the continuously variable transmission before commencement of clutch-to-clutch shifting between the friction clutches when switching the torque transmission route from the route including the geared transmission to the route including the continuously variable transmission.

The vehicle control method may further comprise starting the speed change operation of the continuously variable transmission when switching the torque transmission route, before starting disengagement of the first friction clutch or before starting engagement of the second friction clutch.

The vehicle control method may further comprise carrying out clutch-to-clutch shifting of the friction clutch while changing a speed ratio of the continuously variable transmission.

The vehicle control method may further comprise stopping the speed change operation of the continuously variable transmission before a commencement of an inertia phase resulting from the clutch-to-clutch shifting between the friction clutches.

The vehicle control method may further comprise restarting speed change operation of the continuously variable transmission before completion of the clutch-to-clutch shifting of the friction clutch.

The vehicle control method may further comprise restarting the speed change operation of the continuously variable transmission when a torque transmitting capacity of the second friction clutch exceeds a predetermined value.

As described, the continuously variable transmission may include a pair of pulleys. The vehicle control method may further comprise restarting the speed change operation of the continuously variable transmission when a difference between a rotational speed of the output shaft and a rotational speed of driven pulley of the continuously variable transmission falls below a predetermined value.

As also described, each of the first friction clutch and the second friction clutch individually may include a hydraulic actuator. The vehicle control method may further comprise restarting the speed change operation of the continuously variable transmission when a hydraulic pressure of the second friction clutch exceeds a predetermined level.

Thus, according to the present invention, the speed change operation of the continuously variable transmission is started before torque transmitting capacity of the friction clutch to be brought into engagement starts to be increased to shift the transmission route from the route including the geared transmission to the route including the continuously variable transmission. Therefore, speed ratio of the continuously variable transmission can be changed to achieve a target ratio without delay so that speed change response can be improved. In addition, since a required time until completion of engagement of the clutch is not increased and a speed change shock is reduced, a load acting on a friction member of the friction clutch can be reduced to elongate lifetime of the friction clutch. In addition, the switching control of the transmission route and the speed change operation of the continuously variable transmission can be executed independently, and hence a complicated control is not required. For this reason, the switching operation of the transmission route can be controlled by the simple control while improving speed change response.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a skeleton diagram showing one example of a speed change unit in which the geared transmission and the continuously variable transmission are arranged parallel to each other.

FIG. 2 is a time chart showing changes in vehicle behavior during switching the power transmission route from the route including the geared transmission to the route including the continuously variable transmission.

FIG. 3 is a time chart showing changes in vehicle behavior during switching the power transmission route from the route including the geared transmission to the route including the continuously variable transmission in another control example.

FIG. 4 is a table showing engagement states of the clutch devices and the brake device under each running condition of the vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Preferred example of the present invention will be explained hereinafter. The vehicle control system according to the present invention is applied to a vehicle comprising a continuously variable transmission adapted to change a speed ratio continuously and a geared transmission adapted to select a gear stage from a plurality of fixed stages. In the vehicle, the continuously variable transmission and the geared transmission are arranged parallel to each other between an input shaft to which a power of a prime move is delivered and an output shaft. The vehicle further comprises a clutch device adapted to switch a power transmission route from a route including the continuously variable transmission and a route including the geared transmission. The present invention is configured to actuate the clutch device while activating the continuously variable transmission when switching the power transmission route from the route including the geared transmission to the route including the continuously variable transmission.

Referring now to FIG. 1, there is shown one example of a power transmission route from a prime mover to drive wheels via a speed change unit to which the present invention is applied. The speed change unit is adapted to change a speed ratio between a rotational speed N_(in) of an input shaft 4 and a rotational speed N_(out) of an output shaft 8, and to this end, the speed change unit comprises a torque reversing device 5, a continuously variable transmission 7, and a geared transmission 20. According to the preferred example, an internal combustion engine (E/G) such as a gasoline engine is used as a prime mover. In the following description, the prime mover is called as the “engine 1”.

A torque converter 3 having a lockup clutch is connected to a crank shaft 2 of the engine 1. The torque converter 3 as a conventional fluid coupling comprises a front cover 3 a, a pump impeller 3 b integrated with the front cover 3 a, a turbine runner 3 c opposed to the pump impeller 3 b, and a stator 3 d mounted on a not shown one-way clutch between the pump impeller 3 b and the turbine runner 3 c. Specifically, the front cover 3 a is connected to the crank shaft 2 so that the front cover 3 a and the pump impeller 3 b are rotated integrally with the crank shaft 2. The turbine runner 3 c is connected to the input shaft 4 to be rotated integrally therewith. That is, the turbine runner 3 c is rotated at a same speed N_(t) as the rotational speed N_(in) of the input shaft 4. In addition, a lockup clutch 3 e rotated integrally with the turbine runner 3 c is arranged to be opposed to an inner face of the front cover 3 a. The aforementioned one-way clutch is disposed between the stator 3 d and a fixed member such as a casing.

The torque reversing device 5 is disposed on the input shaft 4. Specifically, the torque reversing device 5 is adapted to transmit torque of the input shaft 4 without reversing a direction to propel the vehicle in the forward direction, and to transmit torque of the input shaft 4 while reversing a direction to propel the vehicle in the backward direction. To this end, a conventional differential mechanism adapted to perform a differential action among three rotary elements is used as the torque reversing device 5. As shown in FIG. 1, according to the preferred example, a double-pinion planetary gear unit is used as the torque reversing device 5.

The torque reversing device 5 comprises a sun gear 5 s as an external gear, a ring gear 5 r as an internal gear that is arranged concentrically with the sun gear 5 s, first pinion gears 5P₁ individually meshing with the sun gear 5 s, second pinion gears 5P₂ individually meshing with the first pinion gears 5P₁ and the ring gear 5 r, and a carrier 5 r supporting the first pinion gears 5P₁ and the second pinion gears 5P₂ in such a manner to revolve around the sun gear 5 s while rotating. The sun gear 5 s is fitted onto the input shaft 4 in such a manner to be rotated integrally therewith to serve as an input element of the planetary gear unit. A rotation of the ring gear 5 r is selectively stopped by a brake device B. That is, the ring gear 5 r serves as a reaction element of the planetary gear unit. The brake device B is disposed between the ring gear 5 r and the fixed member such as the casing, and for example, a multi-plate brake, a friction brake, a dog brake and so on may be used as the brake device B.

The carrier 5 c is rotated integrally with a below-mentioned drive gear 21 of the geared transmission 20 to serve as an output element of the planetary gear unit. In order to rotate the planetary gear unit entirely integrally by connecting the carrier 5 c with the sun gear 5 s, a first clutch device C₁ is disposed between the carrier 5 c and the sun gear 5 s. Specifically, the first clutch device C₁ is adapted to connect and interrupt the input shaft 4 and the geared transmission 20. The first clutch device C₁ is further adapted to deliver the torque of the input shaft 4 directly to the carrier 5 c as the output element. That is, the first clutch device C₁ is disposed to selectively enable and disable torque transmission between the input shaft 4 and the geared transmission 20. According to the preferred example, a wet-type or dry-type friction clutch whose torque transmitting capacity is changed according to an engagement pressure is used as the first clutch device C₁. The first clutch device C₁ is provided with a hydraulic actuator connected to a not shown hydraulic circuit so that the first clutch device C₁ is actuated by changing a hydraulic pressure P_(C1) in the hydraulic actuator. That is, torque transmitting capacity of the first clutch device C₁ is changed by changing hydraulic pressure (i.e., engagement pressure) P_(C1) applied thereto.

The planetary gear unit employed as the torque reversing device 5 can be explained in the form of nomographic diagram. In the nomographic diagram, three vertical lines drawn parallel to one another represent the sun gear 5 s, the ring gear 5 s and the carrier 5 c respectively. Specifically, the line representing the sun gear 5 s and the line representing the carrier 5 c are situated both sides, and the line representing the ring gear 5 r as the reaction element is situated in the middle. Provided that a clearance between the lines representing the sun gear 5 s and the carrier 5 c is “1”, a clearance between the lines representing the ring gear 5 r and the carrier 5 s is determined based on a gear ratio between the sun gear 5 s and the ring gear 5 r. A horizontal base line represents a fact that rotational speeds of those rotary elements are zero, and rotational speeds of the rotary elements are indicated as vertical levels on the vertical lines. Therefore, the rotational speed and a rotating direction of each rotating element in the planetary gear unit can be expressed by the nomographic diagram.

The input shaft 4 and the output shaft 8 are arranged parallel to each other. In the vehicle to which the present invention is applied, a transmission route including a continuously variable transmission 7 adapted to change a speed ratio continuously and a transmission route including the geared transmission 20 adapted to establish a fixed gear stage are arranged parallel to each other. In the following description, a speed ratio of the continuously variable transmission 7 will be called the variable ratio γ₁, and a gear ratio of the geared transmission 20 will be called the fixed ratio γ₂.

A conventional belt-driven continuously variable transmission is used as the continuously variable transmission 7. Specifically, the continuously variable transmission 7 comprises a primary shaft 6 and a secondary shaft 44 arranged parallel to each other, a primary pulley 30 as a drive member rotated integrally with the primary shaft 6, a secondary pulley 40 as a driven member rotated integrally with the secondary shaft 44, and a belt 7 a running on those pulleys 30 and 40. An effective running diameter of the belt 7 a in each pulley 30, 40 is changed by changing a width of a belt groove on the pulley. That is, the variable ratio γ₁ can be changed continuously and steplessly by changing a belt groove of the pulley.

The primary pulley 30 is situated on the other side of the engine 1 in the axial direction across the torque reversing device 5, and rotated integrally with the primary shaft 6 extending coaxially with the input shaft 4. According to the preferred example, the primary shaft 6 and the input shaft 4 are rotated integrally, that is, the primary shaft 6 is rotated integrally with the sun gear 5 s of the torque reversing device 5. The primary pulley 30 comprises a fixed sheave 31 integrated with the primary shaft 6, and a movable sheave 32 fitted onto the primary shaft 6 while being allowed to reciprocate toward and away from the fixed sheave 31. In addition, the movable sheave 32 is provided with an actuator 33 for applying a thrust force to move the movable sheave 32 toward the fixed sheave 31. Specifically, the actuator 33 is attached to a back side of the movable sheave 32, that is, to the opposite side of the fixed sheave 31. Both an electric actuator and a hydraulic actuator may be used as the actuator 33 to push the movable sheave 32 in the axial direction. Since the primary shaft 6 is thus connected to the input shaft 4 to be rotated integrally therewith in the preferred example, the primary shaft 4 will also be called the input shaft 4 in the following description.

The secondary pulley 40 is arranged in such a manner that a rotational center axis thereof extends parallel to that of the primary pulley 30. The secondary pulley 40 comprises a fixed sheave 41 integrated with the secondary shaft 44, and a movable sheave 42 fitted onto the secondary shaft 44 while being allowed to reciprocate toward and away from the fixed sheave 41. In addition, the movable sheave 42 is provided with an actuator 43 for applying a thrust force to move the movable sheave 42 toward the fixed sheave 41. Specifically, the actuator 43 is attached to a back side of the movable sheave 42, that is, to the opposite side of the fixed sheave 41. Both an electric actuator and a hydraulic actuator may also be used as the actuator 43 to push the movable sheave 42 in the axial direction.

A second clutch device C₂ is disposed between the secondary pulley 40 and the output shaft 8 to selectively connect the secondary shaft 44 to the output shaft 8. The second clutch device C₂ is adapted to deliver torque of the secondary shaft 44 directly to the output shaft 8. That is, the second clutch device C₂ selectively enables torque transmission between the continuously variable transmission 7 and the output shaft 8. According to the preferred example, a wet-type or dry-type friction clutch whose torque transmitting capacity is changed according to an engagement pressure may also be used as the second clutch device C₂. The second clutch device C₂ is also provided with a hydraulic actuator connected to a not shown hydraulic circuit so that the second clutch device C₂ is actuated by changing a hydraulic pressure P_(C2) in the hydraulic actuator. That is, torque transmitting capacity of the second clutch device C₂ is changed by changing hydraulic pressure (i.e., engagement pressure) P_(C2) applied thereto. Optionally, the hydraulic actuator of the second clutch device C₂ may be connected to a not shown accumulator.

Here will be explained the geared transmission 20 adapted to shift a gear stage among a plurality of fixed stages. The geared transmission 20 may serve not only as a speed reducing device establishing the fixed ratio γ₂ that is larger than the maximum ratio γ_(1max) of the continuously variable transmission 7, but also as a speed increasing device establishing the fixed ratio γ₂ that is smaller than the minimum ratio γ_(1min) of the continuously variable transmission 7. As shown in FIG. 1, according to the preferred example, the geared transmission 20 is adapted to serve as the speed reducing device. To this end, a counter shaft 23 is disposed between the input shaft 4 and the output shaft 8 to rotate a drive gear 21 of drive side and a driven gear 25 of driven side in a same direction. Specifically, the drive gear 21 is connected to the carrier 5 c as the output member of the torque reversing device 5 while being meshed with a counter driven gear 22 that is diametrically larger than the drive gear 21. Thus, the drive gear 21 and the counter driven gear 22 form a first gear pair. Number of teeth of the counter driven gear 22 is larger than that of the drive gear 21 so that the torque is delivered from the drive gear 21 to the counter driven gear 22 while reducing a rotational speed.

A counter drive gear 24 that is diametrically smaller than the counter driven gear 22 is meshed with a driven gear 25 to form a second gear pair. The counter drive gear 24 is also diametrically smaller than the driven gear 25. That is, number of teeth of the counter drive gear 24 is smaller than that of the driven gear 25 so that the torque is delivered from the counter drive gear 24 to the driven gear 25 while reducing a rotational speed. The driven gear 25 is fitted onto the output shaft 8 while being allowed to rotate relatively therewith, and the driven gear 25 is connected to the output shaft 8 by a below-mentioned third clutch device C₃ to be rotated integrally therewith. Thus, in the geared transmission 20, the drive gear 21 and the output shaft 8 are rotated in a same direction. Accordingly, the fixed ratio γ₂ of the geared transmission 20 is determined by multiplying a speed ratio (i.e., a gear ratio i1) between the drive gear 21 and the counter driven gear 22 by a speed ratio (i.e., a gear ratio i2) between the counter drive gear 24 and the driven gear 25. As described, the fixed ratio γ₂ of the geared transmission 20 thus determined is larger than the maximum ratio γ₁ max of the continuously variable transmission 7.

The third clutch device C₃ is disposed between the driven gear 25 and the output shaft 8 to selectively provide a connection therebetween. That is, the third clutch device C₃ selectively enables torque transmission between the geared transmission 20 and the output shaft 8. Thus in the transmission route including the geared transmission 20, the first clutch device C₁ is disposed on the input shaft 4, and the third clutch device C₃ is disposed on the output shaft 8. As described, the friction clutch is used as the first clutch device C₁ and hence it is unnecessary to change a torque gradually from 0% to 100%. Therefore, a dog clutch such as a synchromesh adapted to be brought into engagement without slip is used as the third clutch device C₃.

The third clutch device C₃ shown in FIG. 1 is a synchronizer adapted to frictionally synchronize a rotational speed of the output shaft 8 to that of the driven gear 25. To this end, a sleeve 53 of the third clutch device C₃ is axially reciprocated by a not shown electrically controlled actuator. Specifically, the driven gear 25 is connected to the output shaft 8 by engaging a spline formed on an inner face of the sleeve 53 of the third clutch device C₃ to both splines of a clutch gear 55 rotated integrally with the driven gear 25 and a hub 51 rotated integrally with the output shaft 8.

The speed change unit shown in FIG. 1 is applied to a front-engine front-wheel drive layout vehicle in which a torque is delivered from the output shaft 8 to a front differential unit 12 as a final reduction through a reduction gear unit 10. Specifically, an output gear 9 is fitted onto the output shaft 8, and a large-diameter gear 10 fitted onto a reduction gear shaft 10 b is meshed with the output gear 9. A diametrically-small gear 10 c is also fitted onto the reduction gear shaft 10 b to be meshed with a ring gear 11 of the front differential unit 12. The torque delivered to the front differential unit 12 via the ring gear 11 is distributed to both drive wheels through each drive shaft 13.

An engagement action of each clutch device C₁, C₂ and C₃, and a speed change operation of the continuously variable transmission 7 are controlled by a not shown electronic control unit (ECU) as a controller. The electronic control unit is a microcomputer comprised of a central processing unit (CPU), memory devices (RAM and ROM), and an input-output interface. Various signals from not shown sensors are sent to the electronic control unit. For example, detection signals of a speed N_(e), of the engine 1, a speed N_(t) of the turbine runner 3 c, a speed N_(in) of the input shaft 4, a speed of the primary shaft 6, a groove width of the primary pulley 30, a groove width of the secondary pulley 40, a speed N_(p2) of the secondary pulley 40, a speed N_(out) of the output shaft 8, a speed of the drive shaft 13, a speed of the drive wheel, a pressure P_(C1) applied to the first clutch device C₁, a pressure P_(C2) applied to the second clutch device C₂, an opening degree Acc of an accelerator, a depression of a brake pedal, a vehicle speed V of the vehicle and so on are sent to the electronic control unit. In addition, various kinds of control programs and data are preinstalled to the electronic control unit, and the electronic control unit carries out various kinds of calculations based on the preinstalled programs and data and incident signals. Calculation results are transmitted from the electronic control unit in the form of command signals to carry out the controls.

According to the preferred example, specifically, the electronic control unit calculates a required drive force based on an opening degree Acc of the accelerator and a vehicle speed V and controls the vehicle to achieve the calculated required drive force. In addition, the electronic control unit switches the transmission route between the route including the geared transmission 20 and the route including the continuously variable transmission 7, and executes a speed change operation of the continuously variable transmission 7 based on the opening degree Acc of the accelerator and the vehicle speed V Specifically, the electronic control unit transmits command signals for actuating the clutch devices C₁, C₂ and C₃ to switch the transmission route from the route including the geared transmission 20 to the route including the continuously variable transmission, or from the route including the continuously variable transmission 7 to the route including the geared transmission 20.

For example, the torque is delivered from the input shaft 4 to the output shaft 8 via the route including the geared transmission 20 when the vehicle is started in the forward direction or propelled in the backward direction. By contrast, when the speed of the vehicle propelled in the forward direction is raised to a certain level, the torque is delivered from the input shaft 4 to the output shaft 8 via the route including the continuously variable transmission 7. Turning to FIG. 4, there is shown a table indicating engagement states of the clutch devices C₁, C₂ and C₃, and the brake device B1 under each running condition of the vehicle. In FIG. 4, “ON” represents an engagement of the engagement device, and “OFF” represents a disengagement of the engagement device, and “(ON)” represents a transitional engagement of the engagement device.

When a relatively large drive force is required, for example, when starting the vehicle in the forward direction, the vehicle is propelled under a first mode in which the torque is delivered from the input shaft 4 to the output shaft 8 via the route including the geared transmission 20. In order to establish the first mode, the first clutch device C₁ and the third clutch device C₃ are brought into engagement, and the second clutch device C₂ and the brake device B are brought into disengagement. Consequently, torque of the engine 1 is delivered to the sun gear 5 s of the torque reversing device 5 through the input shaft 4, and further delivered from the input shaft 4 to the carrier 5 c through the first clutch device C₁ in engagement. In this situation, two rotary elements of the torque reversing device 5 as a planetary gear unit are connected by the first clutch device C₁ so that the torque reversing device 5 is rotated entirely integrally to transmit the torque of the input shaft 4 from the carrier 5 c as the output element to the drive gear 21 of the geared transmission 20 without increasing and decreasing a speed.

Meanwhile, the driven gear 25 of the geared transmission 20 is connected to the output shaft 8 by the third clutch device C₃ so that the torque of the engine 1 can be delivered from the input shaft 4 to the output shaft 8 through the geared transmission 20. In this situation, the geared transmission 20 reduces the rotational speed, that is, multiplies the transmission torque, and the torque thus multiplied is delivered to the output shaft 8 to rotate the output shaft 8 in the forward direction. In this case, a total speed ratio γ₄ of the speed change unit between the speed N_(in) of the input shaft 4 and the speed N_(out) of the output shaft 8 can be calculated by multiplying the fixed ratio γ₂ of the geared transmission 20 by a ratio γ₃ of the torque reversing device 5 as the planetary gear unit. As described, according to the preferred example, the fixed ratio γ₂ is larger than the maximum variable ratio γ_(1max). Thus, when starting the vehicle in the forward direction, the torque reversing device 5 is rotated entirely integrally, and hence the total speed ratio γ₄ is expressed as the fixed ratio γ₂ that is larger than the maximum variable ratio γ_(1max). In this case, the torque of the output shaft 8 is delivered to both drive wheels through the output gear 9, the reduction gear unit 10 and the front differential unit 12 while being multiplied to start the vehicle.

According to the preferred example, the continuously variable transmission 7 is always connected to the input shaft 4 and the sun gear 5 s through the primary shaft 6 even during delivering the torque through the route including the geared transmission 20. In this situation, the torque of the engine 1 is delivered to the pulleys 30 and 40 of the continuously variable transmission 7. However, when starting the vehicle, the second clutch device C₂ is brought into disengagement to interrupt torque transmission between the secondary shaft 44 and the output shaft 8. That is, while the torque is delivered through the route including the geared transmission 20, the torque is not transmitted from the input shaft 4 to the output shaft 8 through the continuously variable transmission 7 and hence an occurrence of an interlocking of the speed change unit can be prevented.

When the vehicle speed V is raised to a predetermined level after starting the vehicle in the forward direction, the running mode of the vehicle is switched from the first mode in which the torque is delivered from the input shaft 4 to the output shaft 8 through the route including the geared transmission 20 to a second mode in which the torque is delivered from the input shaft 4 to the output shaft 8 through the route including the continuously variable transmission 7. In this situation, the running mode of the vehicle is switched from the first mode to the second mode by a clutch-to-clutch shifting from the first clutch device C₁ to the second clutch device C₂. Specifically, the torque transmission route from the input shaft 4 to the output shaft 8 is switched from the route including the geared transmission 20 to the route including the continuously variable transmission 7 by bringing the first clutch device C₁ in engagement into disengagement while bringing the second clutch device C₂ in disengagement into engagement. As described, since the fixed ratio γ₂ is larger than the maximum variable ratio γ_(1max), the total speed ratio γ₄ or the driving force will be changed as a result of switching the torque transmission route from the route including the geared transmission 20 to the route including the continuously variable transmission 7. In order to suppress a shift shock and to prevent discomfort by changing the torque of the output shaft 8 smoothly, the first clutch device C₁ is brought into disengagement while causing a slip, and the second clutch device C₂ is brought into engagement while causing a slip. That is, a torque transmitting capacity of the second clutch device C₂ is increased gradually by increasing an engagement pressure thereof gradually, and a torque transmitting capacity of the first clutch device C₁ is reduced gradually by reducing an engagement pressure thereof gradually. Thus, the torque transmission route is shifted from the route including the geared transmission 20 to the route including the continuously variable transmission 7 by the known clutch-to-clutch shifting from the first clutch device C₁ to the second clutch device C₂.

Here will be explained the switching control of the transmission route carried out by the electronic control unit and vehicle behaviors during the switching control with reference to FIG. 2. In the vehicle before carrying out the switching control, that is, before point t1 shown in FIG. 2, the maximum variable ratio γ_(1max) is set in the continuously variable transmission 7, and the total speed ratio γ₄ of the speed change unit is larger than the maximum variable ratio γ_(1max). In this situation, the engagement pressure P_(C1) applied to the first clutch device C₁ is raised to a level to bring the first clutch device C₁ into engaged completely, and the engagement pressure P_(C2) to the second clutch device C₂ is reduced to zero so that the second clutch device C₂ is brought into disengagement completely. Consequently, the secondary pulley 40 is rotated relatively with the output shaft 8 at the speed N_(p2) that is higher than a rotational speed N_(out) of the output shaft 8. Specifically, the switching control of the transmission route is carried out during upshifting for increasing a rotational speed of the output shaft 8. Moreover, the engagement or the disengagement of each clutch device C₁ and C₂ and the brake device B, and the speed change operation of the continuously variable transmission 7 are executed independently. Therefore, the switching control of the transmission route by controlling the engagement and the disengagement and the speed change operation of the continuously variable transmission 7 are independently controlled by the electronic control unit.

Specifically, when it is determined that there is a request to adjust the total speed ratio γ₄ to be smaller than the maximum speed ratio γ_(1max), or there is a request to adjust the input shaft rotational speed N_(in) (or the engine speed N_(e) or the turbine speed N_(t)) to be lower than the input shaft rotational speed N_(in) based on the total speed ratio γ₄, the electronic control unit transmits a command signal for starting a speed change operation of the continuously variable transmission 7 and a command signal for switching the power transmission route from the transmission route including the geared transmission 20 to the transmission route including the continuously variable transmission 7. The electronic control unit outputs the command signal for switching the transmission route after outputting the command signal for controlling the speed change operation of the continuously variable transmission 7 when it is determined that there is the aforementioned request. The speed change operation of the continuously variable transmission 7 is a control for decreasing the variable speed ratio γ₁, that is, a control for narrowing the groove width of the primary pulley 30. Specifically, the electronic control unit outputs a command signal for operating the actuator 33 and changes the groove width of the primary pulley 30 through electric control or hydraulic control of the actuator 33. The electronic control unit may be configured to transmit a command signal for starting the speed change operation of the continuously variable transmission 7 and a command signal for switching the power transmission route, when it is determined that the increased vehicle speed V has reached a predetermined speed during forward running in which the torque is transmitted through the transmission route including the geared transmission 20, or when it is determined that the rotational speed N_(out) of the output shaft 8 has reached a predetermined speed. Thus, the electronic control unit is configured to start the speed change operation of the continuously variable transmission 7 before the commencement of the clutch-to clutch shifting.

At point t₁ shown in FIG. 2, the speed change operation of the continuously variable transmission 7 is started. That is, the variable ratio γ₁ of the continuously variable transmission 7 starts to decrease at point t₁. Specifically, in the state in which the variable ratio γ₁ is set to the maximum ratio γ_(1max) or a speed ratio close to the maximum ratio γ_(1max), a speed change operation for decreasing the variable speed ratio γ₁ is started. Specifically, an upshifting of the continuously variable transmission 7 is carried out. Here, an actual variable ratio γ_(i) of the continuously variable transmission 7 is changed toward the target ratio at a greater rate (i.e., at a faster speed) in the beginning of speed change operation of the continuously variable transmission 7. For example, if the variable ratio γ₁ of the continuously variable transmission 7 is increased to the maximum variable ratio γ_(1max), the variable ratio γ₁ is reduced toward the target ratio abruptly immediately after the commencement of the speed change operation, and then reduced mildly to achieve the target ratio. That is, in this speed change operation, the change rate (or reduction rate) of the variable ratio γ₁ is the largest immediately after starting the speed change operation and its change rate gradually decreases in a process of change toward the target speed ratio.

Then, at point t₂, during the speed change operation of the continuously variable transmission 7, the clutch-to-clutch shifting is commenced. That is, in a state in which the speed change operation has progressed to some degree, that is, in a state in which the reduction rate of the variable speed ratio γ₁ of the continuously variable transmission 7 is relatively small, the hydraulic pressure P_(C1) of the first clutch device C₁ raised to achieve the complete engagement starts lowering. Then, at point t₃, the hydraulic pressure P_(C2) of the second clutch device C₂ in disengagement starts increasing. Consequently, both the first clutch device C₁ and the second clutch device C₂ start slipping so that the torque transmitting capacity of the first clutch device C₁ starts reducing with the reduction in the engagement pressure P_(C1) applied thereto, and the torque transmitting capacity of the second clutch device C₂ starts increasing with the rise in the engagement pressure P_(C2) applied thereto from zero. Optionally, in the initial phase of the clutch-to-clutch shifting, the engagement pressure P_(C2) applied to the second clutch device C₂ may also be raised while maintaining the engagement pressure P_(C1) to maintain the first clutch device C₁ into complete engagement.

The electronic control unit is further configured to determine a target torque transmitting capacity of the second clutch device C₂ when bringing the disengaged second clutch device C₂ into engagement, and to transmit a command signal to achieve the determined target torque transmitting capacity. For example, the electronic control unit is configured to determine a target torque transmitting capacity of the second clutch device C₂ based on an input torque taking account of an inertia torque of an input member of the second clutch device C₂. That is, the target torque transmitting capacity of the second clutch device C₂ is corrected taking account of the inertia torque. Specifically, the electronic control unit is configured to transmit the command signal to achieve a target engagement pressure based on the target torque transmitting capacity to a linear solenoid valve connected to a hydraulic chamber of the second clutch device C₂.

At point t₄, the engagement pressure P_(C1) applied to the first clutch device C₁ is reduced to zero, and the engagement pressure P_(C2) applied to the second clutch device C₂ is raised to a predetermined pressure level. For example, the predetermined pressure level includes a level at which a desired torque transmitting capacity of the second clutch device C₂ is achieved, and a level at which the engagement pressure P_(C2) applied to the second clutch device C₂ starts being increased by a not shown accumulator. Thus, at point t₄, the first clutch device C₁ is brought into disengagement and the torque transmitting capacity of the second clutch device C₂ is increased to the predetermined value so that an inertia phase of the clutch-to-clutch shifting is commenced. Since an inertial force of the engine 1 is smaller than that of the vehicle 1, the engine speed N_(e) is reduced during the inertia phase and consequently the turbine speed N_(t) equal to the rotational speed N_(in) is reduced. For this reason, when the inertia phase is commenced, the total speed ratio γ₄ between the turbine speed N_(t) and the rotational speed N_(out) of the output shaft starts decreasing. As a result of such reduction in the rotational speed N_(in) of the input shaft 4 while maintaining the variable ratio γ₁ of the continuously variable transmission 7 to the maximum variable ratio γ_(1max), the rotational speed N_(p2) of the secondary pulley 40 is lowered. In a state in which the turbine speed N_(t) increases and in which the total speed ratio γ₄ is constant, if the variable speed ratio γ₁ lowers, the rotational speed N_(p2) of the secondary pulley 40 of the continuously variable transmission 7 increases. Therefore, as illustrated in FIG. 2, the rotational speed N_(p2) of the secondary pulley 40 is increased from the point t₂ to t₄ with a reduction in the variable speed ratio γ₁ at a change rate larger than that of the rotational speed N_(p2) of the secondary pulley 40 under the condition that the variable speed ratio γ₁ is at the maximum speed ratio γ_(1max) before the point t₁.

Then, when the variable speed ratio γ₁ which has been lowering reaches the target speed ratio at point t₅, the speed change operation of the continuously variable transmission 7 is terminated. Specifically, the electronic control unit terminates the speed change operation of the continuously variable transmission 7 during the reduction of the total speed ratio γ₄. That is, the electronic control unit is configured to complete the speed change operation of the continuously variable transmission 7 before completion of the clutch-to-clutch shifting, that is, before the hydraulic pressure P_(c2) is raised to the level at which the second clutch device C₂ is brought into complete engagement. In this case, the electronic control unit may determine whether or not the variable speed ratio γ₁ has become the target speed ratio on the basis of an input signal from a sensor detecting the groove width of the primary pulley 30. That is, the electronic control unit may determine whether or not the variable speed ratio γ₁ has become the target speed ratio by the feedback control.

Moreover, the electronic control unit determines synchronization between rotational speed N_(p2) of the secondary pulley 40 and rotational speed N_(out) of the output shaft. Since a synchronous speed between those members is changed depending on the situation of the speed change operation of the continuously variable transmission 7, the electronic control unit is further configured to determine a synchronization between the rotational speed of those members while observing the situation of the speed change operation of the continuously variable transmission 7 and updating a synchronization judging speed of the second clutch device C₂. That is, the rotational speed N_(p2) of the secondary pulley 40 is changed with a change in the variable ratio γ₁, and hence the electronic control unit observes the situation of the speed change operation of the continuously variable transmission 7 by detecting a speed change rate of the continuously variable transmission 7 or a change rate of the rotational speed N_(p2). Based on the obtained speed change rate of the continuously variable transmission 7 or a change rate of the rotational speed N_(p2), the electronic control unit may calculate the synchronization judging speed of the second clutch device C₂. When a synchronization of the rotational speed N_(p2) of the secondary pulley 40 with the rotational speed N_(out) of the output shaft 8 is determined, the electronic control unit terminates the switching control of the transmission route.

As shown in FIG. 2, the engagement pressure P_(C2) is raised to a level to bring the second clutch device C₂ into complete engagement at point t5 so that the rotational speed N_(p2) of the secondary pulley 40 is synchronized with the rotational speed N_(out) of the output shaft 8. As a result, the switching control of the transmission route, that is, the clutch-to-clutch shifting is completed.

When the switching control of the transmission route is completed, both the brake device 5 and the first clutch device C₁ are brought into disengagement so that the torque reversing device 5 is allowed to rotate freely, and hence the input shaft 4 is disconnected from the geared transmission 20. However, the secondary pulley 40 is connected to the output shaft 8 through the second clutch device C₂ so that the input shaft 4 is connected to the output shaft 8 in such a manner to transmit torque through the continuously variable transmission 7. In the second mode, therefore, a speed of the engine 1 can be adjusted in an optimum fuel efficient manner by gradually reducing a speed ratio of the continuously variable transmission 7 in accordance with a vehicle speed and an opening degree of the accelerator. In case of thus transmitting torque through the route including the continuously variable transmission 7, the total speed ratio γ₄ of the speed change unit is determined by multiplying the ratio γ₃ of the torque reversing device 5 as the planetary gear unit by the variable ratio γ₁. However, the sun gear 5 s as an input element of the torque reversing device 5 is rotated at the same speed as the primary pulley 30 so that the ratio γ₃ thereof is set to 1. In this situation, therefore, the total speed ratio γ₄ of the speed change unit is governed by the variable ratio γ₁.

After the first clutch device C₁ is brought into disengagement and the second clutch device C₂ is brought into engagement so that the torque transmission through the continuously variable transmission 7 is stabilized, the third clutch device C₃ is brought into disengagement to disconnect the geared transmission 20 from the output shaft 8. Consequently, torque is delivered from the input shaft 4 to the sun gear 5 s of the torque reversing device 5. In this situation, since the ring gear 5 r and the carrier 5 c are allowed to rotate freely, the torque reversing device 5 is rotated entirely integrally so that speed differences among the rotary elements thereof are reduced. For this reason, a power loss, a damage, noises and vibrations of the torque reversing device 5 can be reduced. In addition, when the third clutch device C₃ is brought into disengagement, the first clutch device C₁ has already been brought into disengagement and hence torque is not transmitted to the geared transmission 20. In this situation, therefore, the third clutch device C₃ is allowed to be brought into disengagement even if it is a dog clutch.

Next, another control example of the vehicle control system according to the present invention will be described. Referring now to FIG. 3, there are shown the switching control of the transmission route executed by the electronic control unit and behavior of the vehicle Ve during execution of the switching control. In the following description, detailed explanations for the structure similar to those of the foregoing example will be omitted. In FIG. 3, a control and an operation at point T₁ are similar to those at the point t₁ shown in FIG. 2. Similarly, the control and the operations at points T₂, T₃, and T₆ illustrated in FIG. 3 are similar to the control and the operations at the points t₂, t₃, and t₆ shown in FIG. 2.

In this specific example, the change of the variable speed ratio γ₁ is stopped at the point T₄ shown in FIG. 3. Specifically, the electronic control unit outputs a command signal for stopping the speed change operation of the continuously variable transmission 7 when the inertia phase starts during the clutch-to-clutch shifting in which the first clutch device C₁ is disengaged and the second clutch device C₂ is engaged. In short, the change of the variable speed ratio γ₁ is stopped when lowering of the total speed ratio γ₄ is started. In the control and the operation at the point T₄ illustrated in FIG. 3, the hydraulic pressure P_(C1) of the first clutch device C₁ is reduced to zero and the hydraulic pressure P_(C2) of the second clutch device C₂ is raised to a predetermined hydraulic pressure as the control and the operation at the point t₄ shown in FIG. 2.

The electronic control unit is further configured to transmit a command signal for starting a speed change operation of the continuously variable transmission 7 during execution of the clutch-to-clutch shifting. Specifically, the electronic control unit transmits the command signal for starting a speed change operation at a timing between the commencement and completion of the clutch-to-clutch shifting. For example, the electronic control unit transmits the command signal for starting a speed change operation when a difference between the total speed ratio γ₄ and the maximum variable ratio γ_(1max) of the continuously variable transmission 7 becomes smaller than a predetermined value, or when a difference between the rotational speed N_(p2) of the secondary pulley 40 and the rotational speed N_(out) of the output shaft 8 becomes smaller than a predetermined value. Instead, the electronic control unit may also be configured to transmit the command signal for starting a speed change operation when a difference between the current engagement pressure P_(C2) applied to the second clutch device C₂ and the engagement pressure P_(C2) to bring the second clutch device C₂ into complete engagement becomes smaller than a predetermined value. Further, the electronic control unit may also be configured to transmit the command signal for starting a speed change operation when a difference between the current torque transmitting capacity of the second clutch device C₂ and the torque transmitting capacity of the second clutch device C₂ in complete engagement becomes smaller than a predetermined value. That is, the continuously variable transmission 7 is controlled to start a speed change operation before completion of the clutch-to-clutch shifting, and the speed change operation of the continuously variable transmission 7 is preferably started at a timing just before the completion of the clutch-to-clutch shifting.

As illustrated in FIG. 3, at the point T₅, the speed change operation of the continuously variable transmission 7 is restarted, and the variable speed ratio γ₁ starts to decrease again. Moreover, in the beginning of the restart of the speed change operation of the continuously variable transmission 7, the change rate (change speed) of the actual variable speed ratio γ₁ of the continuously variable transmission 7 with respect to the target speed ratio of the continuously variable transmission 7 is increased.

After the restarting of the speed change operation of the continuously variable transmission 7, the electronic control unit carries out a synchronization control of a speed change rate of the continuously variable transmission 7 to a shifting rate of the clutch-to-clutch shifting when the second clutch device C₂ is brought into engagement completely. In other words, the electronic control unit carries out a synchronization of a change rate of the total speed ratio γ₄ with a change rate of the variable ratio γ₁ of the continuously variable transmission 7. To this end, the electronic control unit detects the change rate of the variable ratio γ₁ of the continuously variable transmission 7 by detecting a groove width of the primary pulley 30, and transmits a command signal to change the engagement pressure P_(C2) applied to the second clutch device C₂ in accordance with the detected change rate of the variable ratio γ₁. Otherwise, if the actuator 33 is an electric actuator, the electronic control unit transmits a command signal to the actuator 33 based on the detected change rate of the variable ratio γ₁, and changes the engagement pressure P_(C2) applied to the second clutch device C₂ in such a manner that a change rate of the total speed ratio γ₄ is equalized to that of the variable ratio γ₁. By contrast, if the actuator 33 is a hydraulic actuator, it is also possible to transmit the command signal from the electronic control unit to the hydraulic circuit based on the detected change rate of the variable ratio γ₁.

As can be seen from FIG. 3, during a period from the point T₅ when the speed change operation of the continuously variable transmission 7 is started to the point T₆ when the clutch-to-clutch shifting is completed, the electronic control unit carries out a synchronization of a change rate of the total speed ratio γ₄ with a change rate of the variable ratio γ₁. As a result of thus synchronizing the change rate of the total speed ratio γ₄ with the change rate of the variable ratio γ₁, a speed change operation of the speed change unit can be smoothened. Specifically, in case of delivering torque from the input shaft 4 to the output shaft 8 through the route including the continuously variable transmission 7, the total speed ratio γ₄ of the speed change unit is governed by the variable ratio γ₁. In this case, therefore, the speed change operation of the speed change unit can be carried out smoothly by thus equalizing the change rate of the total speed ratio γ₄ with the change rate of the variable ratio γ₁ when shifting the transmission route from the route including the geared transmission 20 to the route including the continuously variable transmission 7.

As described, the vehicle control system of the present invention is configured to start a speed change operation of the continuously variable unit before starting the clutch-to-clutch shifting to switch the transmission route from the route including the geared transmission to the route including the continuously variable transmission. Therefore, the change rate of the speed ratio of the continuously variable transmission can be changed promptly to the target ratio without delay so that speed change response can be improved. In addition, since the shift shock can be reduced without increasing a required time for the clutch-to-clutch shifting, damage of a friction material of the friction clutch can be reduced to elongate lifetime thereof.

Moreover, in a state in which the change of the speed ratio of the continuously variable transmission is relatively small, the clutch-to-clutch shifting can be executed. That is, in the beginning of the speed change operation of the continuously variable transmission, the clutch-to-clutch shifting has not been started, and hence a complex control is not required to execute the clutch-to-clutch shifting while detecting a change in the rotational speed of the secondary pulley caused by the speed change operation of the continuously variable transmission. Additionally, since the speed change operation of the continuously variable transmission is stopped when the total speed ratio starts to change, the rotational speed of the secondary pulley will not be changed by the speed change operation of the continuously variable transmission. For this reason, a complex control for carrying out the clutch-to-clutch shifting while detecting a change in the rotational speed is not necessary. That is, according to the control device of the present invention, the speed change operation of the continuously variable transmission during execution of the clutch-to-clutch shifting can be simplified.

In the case of propelling the vehicle in the backward direction, as shown in FIG. 4, each clutch devices C₁, C₂, and C₃ and the brake device B is brought into engagement or disengagement. In this case, in the torque reversing device 5, torque of the engine 1 is applied to the sun gear 5 s while halting the ring gear 5 r by the brake device B so that the carrier 5 c is rotated in the opposite direction to the sun gear 5 s. Consequently, as the case of propelling the vehicle in the forward direction, torque is delivered from the input shaft 4 to the output shaft 8 through the geared transmission 20, in the direction to propel the vehicle in the backward direction. In this case, the total speed ratio γ₄ of the speed change unit is determined by multiplying the fixed ratio γ₂ of the geared transmission 20 by the ratio γ₃ of the torque reversing device 5 as the planetary gear unit.

In case of decelerating the vehicle while bringing the first clutch device C₁ and the third clutch device C₃ into engagement, inertia torque of the vehicle would be applied to the output shaft 8. However, since the second clutch device C₂ is brought into disengagement so that the output shaft 8 is disconnected from the secondary pulley 40. In this situation, therefore, a reverse torque resulting from decelerating the vehicle will not be applied to the continuously variable transmission 7. For this reason, the continuously variable transmission 7 can be prevented from being subjected to the unnecessary torque and rotated unnecessarily so that damage of the continuously variable transmission 7 can be reduced. In addition, since the second clutch device C₂ is in disengagement to disconnect the output shaft 8 from the continuously variable transmission 7, an interlocking of the transmission can be prevented.

The speed change unit according to the present invention should not be limited to the foregoing preferred example, and may be modified within the spirit of the present invention.

For example, a single pinion planetary gear unit may also be employed as the torque reversing device instead of the above-explained double pinion planetary gear unit. In case of using the single pinion planetary gear unit as the torque reversing device, specifically, the sun gear 5 s is fitted onto the input shaft 4 while being allowed to rotate relatively therewith to serve as an output element, the carrier 5 c is connected to the brake device B to serve as the reaction element, and the ring gear 5 r is connected to the drive gear 21 to serve as the input element. In this case, the input shaft 4 is connected to the ring gear 5 r, and the sun gear 5 s is connected to the ring gear 5 r by the first clutch device C₁ to be rotated integrally.

Moreover, in order to rotate the torque reversing device integrally, the first clutch device C₁ may also be adapted to connect the sun gear, the carrier and the ring gear to one another, instead of connecting the sun gear to the carrier as in the foregoing example.

Further, any kind of dog clutches such as a key-type synchromesh mechanism, a corn-type synchromesh mechanism, a single corn-type synchromesh mechanism, a multi corn-type synchromesh mechanism etc. may be used as the third clutch device C₃.

Furthermore, the geared transmission may be adapted not only to establish one fixed gear stage (i.e., a gear ratio or a reduction ratio) but also to shift a gear stage among a plurality of fixed stages (i.e., a gear ratio or a reduction ratio). As described, the geared transmission is disposed to deliver torque of the input shaft to the output shaft with a speed ratio which cannot be established by the continuously variable transmission. To this end, any kind of gear unit having a gear pair whose gear ratio is larger than the maximum speed ratio of the continuously variable transmission may be used as the geared transmission.

REFERENCE SIGNS LIST

1: prime mover; 2: output shaft (crank shaft); 4: input shaft; 5: torque reversing device; 5 s: sun gear; 5 r: ring gear; 5P₁: first pinion gear; 5P₂: second pinion gear; 5 c: carrier; 6: primary shaft; 7: continuously variable transmission; 7 a: belt; 8: output shaft; 9: output gear; 10: reduction gear unit; 12: front differential; 13: drive shaft; 20: geared transmission; 21: drive gear; 22: counter driven gear; 23: counter shaft; 24: counter drive gear; 25: driven gear; 30: primary pulley; 40: secondary pulley; 41: fixed sheave; 42: movable sheave; 34: thrust applying mechanism; 44: secondary shaft; B: brake device; C₁: first clutch device (friction clutch); C₂: second clutch device (friction clutch); C₃: third clutch device (dog clutch). 

1. A vehicle control system comprising: a continuously variable transmission for changing a speed ratio continuously that is disposed between an input shaft to which torque of a prime mover is applied and an output shaft; a geared transmission that is disposed parallel to the continuously variable transmission, and that is adapted to establish a speed ratio that is larger than a maximum speed ratio established by the continuously variable transmission; a first friction clutch that is brought into engagement during propelling the vehicle by delivering torque through a route including the geared transmission and brought into disengagement during propelling the vehicle by delivering torque through a route including the continuously variable transmission; and a second friction clutch that is brought into engagement during propelling the vehicle by delivering torque through the route including the continuously variable transmission and brought into disengagement during propelling the vehicle by delivering torque through the route including the geared transmission, wherein the vehicle control system is configured to start a speed change operation of the continuously variable transmission before a commencement of clutch-to-clutch shifting between the friction clutches when switching the torque transmission route from the route including the geared transmission to the route including the continuously variable transmission.
 2. The vehicle control system as claimed in claim 1, wherein the vehicle control system is configured to start the speed change operation of the continuously variable transmission when switching the torque transmission route, before starting disengagement of the first friction clutch or before starting engagement of the second friction clutch.
 3. The vehicle control system as claimed in claim 1, wherein the vehicle control system is configured to execute the clutch-to-clutch shifting between the friction clutches while changing a speed ratio of the continuously variable transmission.
 4. The vehicle control system as claimed in claim 1, wherein the vehicle control system is configured to stop the speed change operation of the continuously variable transmission before a commencement of an inertia phase resulting from the clutch-to-clutch shifting between the friction clutches.
 5. The vehicle control system as claimed in claim 4, wherein the vehicle control system is configured to restart the speed change operation of the continuously variable transmission before completion of the clutch-to-clutch shifting between the friction clutches.
 6. The vehicle control system as claimed in claim 5, wherein the vehicle control system is configured to restart the speed change operation of the continuously variable transmission if a torque transmitting capacity of the second friction clutch is greater than a predetermined value.
 7. The vehicle control system as claimed in claim 5, wherein the continuously variable transmission includes a pair of pulleys; and wherein the vehicle control system is configured to restart the speed change operation of the continuously variable transmission when a difference between a rotational speed of the output shaft and a rotational speed of driven pulley of the continuously variable transmission is smaller than a predetermined value.
 8. The vehicle control system as claimed in claim 5, wherein each of the first friction clutch and the second friction clutch individually includes a hydraulic actuator; and wherein the vehicle control system is configured to restart the speed change operation of the continuously variable transmission when a hydraulic pressure of the second friction clutch is higher than a predetermined level.
 9. A control method of a vehicle comprising: a continuously variable transmission for changing a speed ratio continuously that is disposed between an input shaft to which torque of a prime mover is applied and an output shaft; a geared transmission that is disposed parallel to the continuously variable transmission, and that is adapted to establish a speed ratio that is larger than a maximum speed ratio established by the continuously variable transmission; a first friction clutch that is brought into engagement during propelling the vehicle by delivering torque through a route including the geared transmission and brought into disengagement during propelling the vehicle by delivering torque through a route including the continuously variable transmission; and a second friction clutch that is brought into engagement during propelling the vehicle by delivering torque through the route including the continuously variable transmission and brought into disengagement during propelling the vehicle by delivering torque through the route including the geared transmission, the vehicle control method is characterized by comprising: starting a speed change operation of the continuously variable transmission before commencement of clutch-to-clutch shifting between the friction clutches when switching the torque transmission route from the route including the geared transmission to the route including the continuously variable transmission.
 10. The vehicle control method as claimed in claim 9, further comprising: starting the speed change operation of the continuously variable transmission when switching the torque transmission route, before starting disengagement of the first friction clutch or before starting engagement of the second friction clutch.
 11. The vehicle control method as claimed in claim 9, further comprising: carrying out clutch-to-clutch shifting of the friction clutch while changing a speed ratio of the continuously variable transmission.
 12. The vehicle control method as claimed in claim 9, further comprising: stopping the speed change operation of the continuously variable transmission before a commencement of an inertia phase resulting from the clutch-to-clutch shifting between the friction clutches.
 13. The vehicle control method as claimed in claim 12, further comprising: restarting speed change operation of the continuously variable transmission before completion of the clutch-to-clutch shifting of the friction clutch.
 14. The vehicle control method as claimed in claim 13, further comprising: restarting the speed change operation of the continuously variable transmission when a torque transmitting capacity of the second friction clutch exceeds a predetermined value.
 15. The vehicle control method as claimed in claim 13, wherein the continuously variable transmission includes a pair of pulleys; and further comprising restarting the speed change operation of the continuously variable transmission when a difference between a rotational speed of the output shaft and a rotational speed of driven pulley of the continuously variable transmission falls below a predetermined value.
 16. The vehicle control method as claimed in claim 13, wherein wherein each of the first friction clutch and the second friction clutch individually includes a hydraulic actuator; and further comprising restarting the speed change operation of the continuously variable transmission when a hydraulic pressure of the second friction clutch exceeds a predetermined level. 